The two-stroke engine is remarkable for its simplicity, for its few moving parts as well as for its reliable construction and operation. Also, its high power to weight ratio makes it ideal for a large number of applications. The structure of this engine is appropriate for the incorporation therein of a multitude of custom-built accessories and for the mounting of the engine in various positions. In the past, the structure of this engine has fascinated many users and challenged the more ingenuous ones to develop performance-enhancing attachments of all sorts.
In regard to the field of the present invention, a number of improvements have been made in the past to influence the movements of gases inside an internal combustion engine. These improvements were designed basically for extracting exhaust gases more efficiently, for reintroducing a nominal quantity of unburnt exhaust gases into the combustion chamber and for compressing an intake charge inside the combustion chamber.
One of the first improvements to the two-cycle engine came in the form of a megaphone or taper pipe mounted on the end of the exhaust pipe. The purpose of this taper pipe is primarily to facilitate the easy exit of burnt gases from the cylinder. Another improvement was obtained when someone placed a reverse megaphone separated by a straight section of pipe in the exhaust system. This particular improvement helped to control the movement of a pressure wave in the exhaust system and to limit the outflow of induced fuel-rich gases through the exhaust port. Since that time, there have been a number of additional improvements made to the taper pipe by changing its length, its cross-section dimensions and the taper angles.
The use of the taper pipe on an exhaust system is also known for improving the efficiency of an engine by timely reflecting a sound wave toward the combustion chamber, thereby stuffing excess air/fuel mixture back into the combustion chamber to be burnt. Depending on the length of the pipe and the temperature of the gasses within the pipe, a manufacturer is able to design an exhaust system for providing maximum power or torque at a specific engine speed (RPM).
However, because of the static nature of the taper pipe concept and the physical constrictions associated with it, it has been difficult in the past to design a system that offers an increase in performance and efficiency over a wide range of operating conditions. It is known for example, that the performance of an engine depends upon the speed of the engine, the degree of opening of the throttle, the speed of sound at various temperatures of the intake/exhaust system, at different atmospheric pressures and at different elevations of the engine. The performance of an engine also depends upon the changes in volume of an exhaust chamber due to build-ups of carbon inside an exhaust pipe, on the wear of an engine or upon other factors of the like.
As such, a number of accessories for improving the performance of internal combustion engines under various operating conditions have been developed in the past and have been used with varying degrees of success. A representative sample of intake/exhaust gases controlling devices of the prior art is explained briefly herein below, and may be better appreciated by reading the following patent documents.
U.S. Pat. No. 3,254,484 issued on Jun. 7, 1966 to John S. Kopper. The system described therein uses sound pressure waves to assist cylinder charging and cylinder scavenging in an internal combustion engine. A first transducer is installed in the intake header and a second transducer is installed in the exhaust header. The transducers are positioned close to the cylinder ports, at right angle with the intake and exhaust passages, and the operation thereof is associated with the intake or exhaust cycle of the engine, for generating sound waves into the exhaust and intake tracts. In order that a pressure wave and a negative pressure pulse arrive at the intake and exhaust ports respectively, at the moment when it will be most beneficial, the intake and exhaust systems have resonating chambers the volumes of which are telescopically adjustable in accordance with variations in engine speed.
U.S. Pat. No. 4,827,880 issued on May 9, 1989 to Masaki Ban et al. This invention relates to a pulsation controller for improving the intake/exhaust systems of internal combustion engines. The controller is connected to sensors for detecting pressure waves travelling in the intake/exhaust systems and has a microprocessor for controlling the timing for opening or closing valves or ports in the intake/exhaust systems according to the phases of these pressure waves, for improving the intake/exhaust efficiencies of the engine.
U.S. Pat. No. 5,050,378 issued on Sep. 24, 1991 to William B. Clemmens. The system described in this document uses the reflected exhaust pressure waves travelling inside the muffler to reintroduce exhaust gases and compress an intake charge into the combustion chamber prior to the compression stroke of the piston. An expansion chamber along the muffler pipe is configured to reflect a sound wave toward the exhaust port. The timing of the wave with the engine speed is done by adjusting the position of a reflection cone inside the expansion chamber, or by injecting fresh air in the exhaust passage to change the temperature of the exhaust gases. The system is believed applicable to engines that are predominantly operated at full power design speed.
U.S. Pat. No. 5,060,271 issued on Oct. 22, 1991 to Earl R. Geddes. This invention comprises a muffler pipe having two transducers and a controller for attenuating the noise of the engine. The transducers are spaced apart and operated in such a way that the sound waves produce a negative pressure at the exhaust port when the exhaust valve opens, to aid the extraction of the combustion gases.
U.S. Pat. No. 5,101,626 issued on Apr. 7, 1992 to Alan J. Blair. The muffler systems described in this document are configured to statically manipulate an acoustical pressure wave produced by the engine to create a negative pressure at the valve port of one piston during its exhaust stroke, and a positive pressure at the port of another piston during its compression stroke.
U.S. Pat. No. 5,245,824 issued on Sep. 21, 1993 to Randy G. Nouis. The document describes a quarter wave tube of optimal length and cross-section area and its placement on a conventional resonant exhaust system to significantly enhance the performance of the engine over a certain range of engine speeds including the peak RPM of the engine.
Canadian Patent 1,032,843 issued on Jun. 13, 1978 to Larry L. Anderson et al. This document describes an exhaust system for an internal combustion engine, and several types of baffle plates positioned in the exhaust pipe for reflecting sound waves travelling in the exhaust pipe, for reducing the effect of these sound waves on the gases in the combustion chamber.
Aside from the invention of Ban et al., the acoustical systems of the prior art are believed to be limited to static systems wherein the efficiency of the engine is directly related to the physical dimensions of a resonating chamber and the wavelength of the sound of an exhaust system. Therefore the efficiencies of the engines using these static acoustical systems are believed to be limited to a narrow range of operating speeds. It is known for example that certain parameters such as gas temperature, needs of the driver or application of the vehicle are subject to change within minutes. Although manufacturers have made every effort to build the best possible systems, the systems of the prior art are believed to be nonetheless a compromise favouring a performance at maximum engine speed over fuel efficiency at common operating conditions.
It is believed that because of the static aspect of exhaust taper pipes, a two-stroke engine having those pipes is efficient over a three to 10 percent of its RPM range. It is further believed that over the remaining ninety to 97 percent of the operating range of an engine, tremendous inefficiencies exist, often caused by the same wave harmonics that created the desired power improvement at higher RPM levels. For the vast majority of engines, except those designed specifically for racing, a great portion of their service life is spent operating at low to medium RPM. It is believed that at lower engine speeds, it is common for sound waves/pulses of an acoustical intake/exhaust system to travel into the combustion chamber, through the transfer port, into the crankcase and out the intake port. This is a tremendous impediment to the flow of gases through the engine.
Therefore, it is believed that a need exists for a better acoustical intake/exhaust system capable of enhancing the efficiency and performance of an internal combustion engine at common engine speeds. It is believed that a need exists for an acoustical intake/exhaust system that is not dependent upon the wavelength of the sound waves in an exhaust system, upon exhaust temperature, atmospheric pressure and upon the shape and dimensions of an exhaust pipe.